The long-term goal of this research project is to understand the molecular basis of cellular adhesion. Currently, we are using a multidisciplinary approach involving biochemical, immunological, and microscopic methods to study the cell surface receptors involved in fibroblast adhesion to fibronectin and to compare fibroblast spreading and phagocytosis. Variants of baby hamster kidney (BHK) cells that are deficient in various stages of cell adhesion to fibronectin have been prepared and are being characterized. One of these variants, FN-01, appears to lack its fibronectin receptors, and the other variant, FN-02, has fibronectin receptors but is deficient at the next step in the adhesion process. In addition, experiments are underway to characterize the cell surface components that are bound by antibodies to BHK cells that block cell adhesion. Finally, experiments have been initiated to prepare monoclonal antibodies to BHK cells that will be screened for their effects on the adhesion process. In the studies on comparing cell spreading and phagocytosis, experiments are underway to determine the interaction of cells spread on fibronectin-coated substrata with fibronectin-coated latex beads of 1, 5, and 15 micron diameters. In particular, the cytoskeletal response of the cells to the beads--monitoring actin, vinculin, alpha-actinin, tropomyosin, and clatherin--is being analyzed. In addition to the above studies, recent findings have demonstrated that Mn ions are able to induce a cell-spreading response that is independent of specific ligands on the substratum surface. Studies to characterize this phenomenon further are in progress. (A)